Assessing the therapeutic potential and selectivity of novel JAK PROTACs in CTCL

Summary: Abstract Body: Cutaneous T-cell lymphoma (CTCL) is a group of rare non-Hodgkin lymphomas driven by the proliferation of malignant, skin-homing T-cells. In advanced stages, CTCL often progresses to systemic disease, becoming fatal with no curative treatments. This highlights an unmet need for more effective, targeted therapies. The JAK/STAT signaling pathway plays a critical role in CTCL progression, making it a compelling therapeutic target. PROTACs (proteolysis-targeting chimeras) are bifunctional molecules that selectively degrade target proteins, offering a novel approach to overcoming resistance associated with small-molecule inhibitors. We conducted preclinical, in vitro screening of 10 newly designed JAK PROTACs by assessing cell death induction (Cell Titer Glo) in CTCL cell lines and patient-derived malignant T-cells. Cell lines MyLa, HH and HUT78 gave highly variable responses to JAK degradation, with HUT78 showing the greatest sensitivity: IC50: 67.06±33.97 nM across all 10 PROTACs. These compounds also exerted potent anti-tumor effects against patient-derived malignant T-cells, exemplified by top performers YW-JK-25 (IC50: 38.25±30.71 nM, N=4), and YW-JK-28 (IC50: 31.47±23.78 nM, N=3). To evaluate potential selectivity of action in malignant vs normal T cells (that may vary in JAK activity dependence), assays were also performed on non-malignant CD4+ control cells and specificity indices (SI: mean IC50 control/IC50 malignant) were calculated, with JAK inhibitor, fedratinib, used for comparison. Several JAK PROTACs demonstrated higher SI than fedratinib, with YW-JK-28 achieving SI = 30.62 vs 0.6880 for fedratinib. These findings highlight the potential of JAK PROTACs to selectively target malignant CTCL cells, providing a foundation for further investigation into their role as promising therapeutic candidates. Monica Torres¹, Wei Yan², Julia Lewis³, Hong-yu Li², Michael Girardi³ 1. School of Medicine, Universidad Central Del Caribe, Bayamón, Puerto Rico. 2. Pharmacology, The University of Texas Health Science Center at San Antonio, San Antonio, TX, United States. 3. Dermatology, Yale University School of Medicine, New Haven, CT, United States. Translational Studies: Cell and Molecular Biology